1. Field of the Invention
The present invention relates to a traveling wave tube having a delay line in the form of a helix which is supported within a metallic sleeve by a plurality of dielectric support rods which extend along the delay line, the delay line being connected at each end thereof to a respective HF energy supply conductor and discharge conductor, and more particularly to such a delay line in which a matching component is provided in the region of at least one of the ends of the delay line and extending in close proximity to the delay line to achieve a low reflection transition between the surge impedance of the delay line and the respective coupling conductor.
2. Description of the Prior Art
In traveling wave tubes, the surge impedances of the interaction section, on the one hand, and of the coupling conductors (generally rectangular wave guides or coaxial lines), on the other hand, differ from each other and in such a manner that it is usually necessary to take special, impedance-transforming measures in order to reduce the reflection factors of wide-band traveling wave tubes to a viable degree. If the delay line consists of a helix, for purposes of impedance matching, frequently metal rings (.lambda./4 transformers) having a length which amounts to approximately one quarter of the average line wave length are placed over the ends of the helix. If transition elements of this kind are to supply favorable matching values, they result in assembly problems and also in production problems as in a narrow space they collide with the support rods, cannot easily be secured, and in practice must frequenty be provided with oblique or curved inner surfaces in an additional operation. For this reason, it has already been disclosed in U.S. Pat. No. 3,729,644 that for impedance transformation the turns of the helix should simply be conductively shunted by a soldered-off longitudinal rod in the region of the coupling conductor. This type of line loading should be comparatively simpler to apply, at least in the case of helical structures of large dimension, but the same is not particularly effective in the case of wide band structures.